The present invention relates to a vapor-temperature control system for an evaporator for controlling an actual temperature of a vapor generated by an evaporator for heating a liquid-phase working medium by an exhaust gas from an engine to a target vapor temperature.
There are vapor-temperature control systems conventionally known from Japanese Utility Model Publication Nos. 2-38161 and 2-38162, wherein in order to vary the amount of water supplied to a waste heat recovery boiler for recovering a heat energy of an exhaust gas from an engine to control an actual vapor temperature to a target vapor temperature, a feedforward control value is calculated based on a throttle opening degree in the engine, and a feedback control value is calculated based on a difference between the actual vapor temperature and the target vapor temperature, whereby the amount of water supplied to the waste heat recovery boiler is controlled by a value resulting from the addition of the feedforward control value and the feedback control value to each other.
For example, in an engine for an automobile, various controls such as a fuel-cut control, an ignition-retarding control, an EGR control and an air fuel ratio control are carried out for the purpose of varying the burned state of the engine and hence, they exert a direct influence to the temperature of an exhaust gas. Therefore, in an engine in which the various controls are carried out, it is difficult to control the temperature of a vapor with a good responsiveness and accurately in a transient state of the engine.
The present invention has been accomplished with the above circumstances in view, and it is an object of the present invention to control the temperature of a vapor generated by an evaporator operated by an exhaust gas from an engine with a high accuracy even in a transient state of the engine.
To achieve the above object, according to a first aspect and feature of the present invention, there is proposed a vapor-temperature control system for an evaporator for controlling an actual temperature of a vapor generated by an evaporator for heating a liquid-phase working medium by an exhaust gas from an engine to a target vapor temperature, characterized in that the system comprises a liquid-phase working medium supply amount varying means for varying the amount of liquid-phase working medium supplied to the evaporator, and a control means for controlling the amount of liquid-phase working medium supplied by the liquid-phase working medium supply amount varying means, based on a parameter indicating the burned state of the engine.
With the above arrangement, when the liquid-phase working medium is supplied to the evaporator operated by the exhaust gas from the engine, the amount of liquid-phase working medium supplied is controlled based on the parameter indicating the burned state of the engine which exerts an influence directly to the temperature of the exhaust gas. Therefore, the actual temperature of the vapor generated by the evaporator can be controlled to the target vapor temperature with a high accuracy even in a transient state of the engine.
According to a second aspect and feature of the present invention, in addition to the first feature, the parameter indicating the burned state of the engine is at least one of a fuel-cut control signal, an ignition-retarding control signal, an EGR control signal and an air fuel ratio control signal.
With the above arrangement, the amount of liquid-phase working medium supplied is controlled based on at least one of the fuel-cut control signal, the ignition-retarding control signal, the EGR control signal and the air fuel ratio control signal. Therefore, the burned state of the engine can be reflected properly, and the actual temperature of the vapor can be controlled with a high accuracy.
According to a third aspect and feature of the present invention, in addition to the first or second feature, the control means includes a feedforward control means for controlling the amount of liquid-phase working medium supplied in accordance with an engine rotational speed and an engine load, and a feedback control means for controlling the amount of liquid-phase working medium supplied, based on a difference between the actual vapor temperature and the target vapor temperature.
With the above arrangement, the following controls are used: the feedforward control for controlling the amount of liquid-phase working medium supplied in accordance with the engine rotational speed and the engine load, and the feedback control for controlling the amount of liquid-phase working medium supplied, based on the difference between the actual vapor temperature and the target vapor temperature. Therefore, it is possible to achieve both of the responsiveness and the convergence of the control for equalizing the actual vapor temperature to the target vapor temperature.
A supplied-water amount control injector 7 in an embodiment corresponds to the liquid-phase working medium supply amount varying means of the present invention; a vapor temperature control unit 11 in the embodiment corresponds to the control means of the present invention; a feedforward control section 17 in the embodiment corresponds to the feedforward control means of the present invention; a feedback control section 18 in the embodiment corresponds to the feedback control means of the present invention; and an intake negative pressure PB in the embodiment corresponds to the engine load of the present invention.